1. Field of the Invention
The present invention relates to a zoom lens for projection and a projection-type display apparatus. For example, the present invention relates to a zoom lens for projection appropriate to magnify and project rays carrying video image information from a light valve onto a screen, and also to a projection-type display apparatus using the zoom lens for projection.
2. Description of the Related Art
Conventionally, projection-type display apparatuses for magnifying and projecting images displayed on light valves, such as a liquid crystal display device and a DMD (Digital Micromirror Device: Registered Trademark), were used during presentation and the like. It is desirable, for example, that a lens for projection mounted on such an apparatus has a long back focus so that a color combination optical system is arrangeable between the light valve and the projection lens. Further, when the angle dependency characteristics of the color combination optical system are taken into consideration, it is desirable that a reduction side is telecentric. When the installation characteristics for indoor space setting are taken into consideration, it is desirable that the structure is compact, and the like.
Further, in recent years, zoom lenses that can change the sizes of images on a screen were often used. Therefore, a zoom lens that can change the size at a high ratio, in other words, a zoom lens with a high zoom ratio is requested. Further, since a widening function for making a large image projectable onto a position close to the projection-type display apparatus is needed, a wider angle of view is also requested. The lens system also needs to have a small F-number, which means the lens system is a fast lens system, to realize a projection-type display apparatus with higher brightness. Further, aberrations also need to be excellently corrected to cope with recent high definition light valves.
To satisfy the aforementioned needs and requests, five-group or six-group zoom lenses for projection have been proposed. As known six-group zoom lenses for projection, zoom lenses are disclosed, for example, in Japanese Unexamined Patent Publication No. 2005-316186 (Patent Document 1), Japanese Unexamined Patent Publication No. 2008-275713 (Patent Document 2), Japanese Unexamined Patent Publication No. 2011-100079 (Patent Document 3), and Japanese Unexamined Patent Publication No. 2010-156762 (Patent Document 4). In the six-group zoom lenses, a first lens group having negative refractive power, and which is fixed during magnification change, is arranged closest to the magnification side, and a sixth lens group having positive refractive power, and which is fixed during magnification change, is arranged closest to the reduction side. Further, four lens groups of second through fifth lens groups that move during magnification change are arranged between the first lens group and the sixth lens group. Further, Japanese Unexamined Patent Publication No. 2011-154339 (Patent Document 5) discloses a five-group zoom lens for projection in which a first lens group having negative refractive power, and which is fixed during magnification change, is arranged closest to the magnification side and a fifth lens group having positive refractive power, and which is fixed during magnification change, is arranged closest to the reduction side. Further, three lens groups of second through fourth lens groups that move during magnification change are arranged between the first lens group and the fifth lens group.